1. Field of the Invention
The present invention relates to a power control circuit for controlling on/off of a power source to an electronic device.
2. Description of the Prior Art
Conventionally, to turn on/off an electronic device, as shown in FIG. 11, a power on/off switch SW1 is provided between a battery BATT1 and a circuit block 54 to directly turn power supply on/off. If an automatic power-off function is required, as shown in FIG. 12, a power device Q1 such as a power MOS and a power transistor is provided between a battery BATT2 and a circuit block 54, and the power device Q1 is turned on or off in response to on or off of a power on/off switch SW2.
When such a power device is used in an electronic device, the power device must be controlled by monitoring a state of a power on/off switch in the electronic device continuously using a microcomputer, for example. In this case, supply of electrical power to a circuit block of the electronic device can be cut off. However, since the microcomputer must monitor the state of the power on/off switch continuously, electrical power is continuously supplied to the microcomputer to maintain the function of the microcomputer. In practice, the microcomputer monitors the state of the power on/off switch by using a power saving mode such as a sleep mode.
In the case of an example as shown in FIG. 12, the electric power supplies to the microcomputer 56 continuously, so the microcomputer 56 monitors a power on/off state of a power on/off switch SW2 via a SW monitoring port continuously.
Here, if the power on/off switch SW2 is turned off, the level of the SW monitoring port becomes low since the SW monitoring port is connected to ground via a resistive element R1. When the microcomputer 56 detects that the level of the SW monitoring port is low, the microcomputer 56 sets a circuit power-supply control port to a high level. Thus, a power device Q1 is turned off, thereby stopping the power supply to a circuit block 54. Namely, a power of the electronic device is turned off.
On the other hand, if the power on/off switch SW2 is turned on, the level of the SW monitoring port becomes high. When the microcomputer 56 detects that the SW monitoring port is a high level, the microcomputer 56 sets the circuit power-supply control port to a low level. Thus, the power device Q1 is turned on, thereby supplying power to the circuit block 54. Namely, a power of the electronic device is turned on.
When the automatic power-off function mentioned above is provided in the electronic device, the electronic device must be constructed to be able to turn on and off of the electronic device by using a controller such as the microcomputer 56.
However, in this configuration, if the power to the microcomputer 56 is turned off, the microcomputer 56 will not be able to turn on the power to the power device Q1, i.e., the power to the electronic device. Therefore, even if the power supply to the circuit block 54 is stopped, the electrical power must be supplied to the microcomputer 56 continuously.
Therefore, if the electronic device is equipped with an automatic power-off function, the controller such as the microcomputer 56 necessarily consumes the electric power. In particular, if the electronic device is battery-operated, there is a disadvantage to shorten an operating time of the electronic device because of power consumption by the controller.
Further, in the conventional electronic device as shown in FIG. 12, two ports, i.e., the SW monitoring port and the circuit power-supply control port, and the microcomputer 56 are need. In addition, as mentioned above, the microcomputer 56 needs a program for controlling a shift to a sleep mode after automatic power off as well as a program for monitoring the state of the power on/off switch SW2 and controlling on and off of the power device Q1 in response to an interrupt process. Therefore, the program for the microcomputer 56 becomes complicated, thus leading to the case that the incidence of bug in the program is increased.
In view of the stated problem of the conventional art, it is therefore an object of the present invention to provide a power control circuit having an automatic power-off function capable of reducing electrical power consumption if the power is turned off, of reducing the number of ports of a microcomputer, and of simplifying program of the microcomputer.
In accordance with one aspect of the present invention, in order to achieve the above object, the present invention is directed to a power control circuit that controls on/off of power of an electronic device including a power section and a predetermined circuit block. The power control circuit of the present invention comprises: a power on/off switch having a first switch and a second switch, the first and second switches adapted to be turned on or off simultaneously; a capacitive element connected to the power section via the first switch, said capacitive element adapted to be charged by the power section via the first switch when said power on/off switch is turned off and to be discharged when said power on/off switch is turned on; a first switching element connected to the power section via the second switch, said first switching element adapted to be turned off when said power on/off switch is turned off, and to be in a power-on state while an electric charge that has been charged in said capacitive element is being discharged when said power on/off switch is turned on; a microcomputer for controlling power on/off of said first switching element; and a second switching element provided between the power section and each of said microcomputer and the predetermined circuit block, said second switching element adapted to be turned off to stop power supply to said microcomputer and the predetermined circuit block when said first switching element is turned off, and to be turned on to supply power to said microcomputer and the predetermined circuit block when said first switching element is turned on. In this case, the microcomputer is programmed to control the power control circuit such that, when supplying power to said microcomputer, said microcomputer holds the power-on state of said first switching element before said first switching element is turned off because of the discharge of the electric charge charged in said capacitive element, and then, when said microcomputer detects that the predetermined circuit block has not operated for a given period of time, said microcomputer turns off said first switching element.
In one preferred embodiment of this invention, it is preferred that the power section includes one or more battery. It is also preferred that the first and second switching elements are transistors.
In this embodiment of the present invention, the power control circuit may further comprise a regulator provided between said second switching element and the predetermined circuit block for stabilizing a power-supply voltage supplied from the power section.
Further, in this embodiment of the present invention, the electronic device may be selected from a printer, a notebook type personal computer, a personal data assistant machine, a handy type game machine, and a battery-operated radio and audio equipment.
If the electronic device is a printer, the printer may be a Cycolor type printer. Also, the printer may comprise a head for exposure on which one or more light sources for emitting red light, one or more light sources for emitting green light, and one or more light sources for emitting blue light are provided. In this case, the printer is constructed to reproduce an image on a photosensitive printing paper by exposing the photosensitive printing paper by means of said head for exposure. Here, the photosensitive printing paper may contain a plurality of photosensitive microcapsules to be exposed by said head for exposure.
Moreover, the printer may further comprise: a first group of registers for setting image data corresponding to the light sources for emitting red light, image data corresponding to the light sources for emitting green light, and image data corresponding to the light sources for emitting blue light; and a second group of registers for holding the image data, which has been set in each of said first group of registers. In this case, the printer is constructed so as to set next image data in said first group of registers and to drive each of the light sources provided on the head for exposure by using the image data that is held in each of said second group of registers in parallel.
In view of the stated problem of the conventional art, it is therefore another object of the present invention to provide a power control circuit having an automatic power-off function capable of reducing electrical power consumption if the power is turned off, and of having a simple structure without a microcomputer.
In another aspect of the present invention, in order to achieve the above object, the present invention is directed to a power control circuit that controls on/off of power of an electronic device including a power section and a predetermined circuit block. The power control circuit of the present invention comprises: a power on/off switch having a first switch and a second switch, the first and second switches adapted to be turned on or off simultaneously; a capacitive element connected to the power section via the first switch, said capacitive element adapted to be charged by the power section via the first switch when said power on/off switch is turned off and to be discharged when said power on/off switch is turned on; a first switching element connected to the power section via the second switch, said first switching element adapted to be turned off when said power on/off switch is turned off, and to be in a power-on state while an electric charge that has been charged in said capacitive element is being discharged when said power on/off switch is turned on; a hard circuit for controlling power on/off of said first switching element; and a second switching element provided between the power section and each of said hard circuit and the predetermined circuit block, the second switching element adapted to be turned off to stop power supply to said hard circuit and the predetermined circuit block when said first switching element is turned off, and to be turned on to supply power to said hard circuit and the predetermined circuit block when said first switching element is turned on. In this case, the power control circuit is constructed such that, when supplying power to said hard circuit, said hard circuit holds the power-on state of said first switching element before said first switching element is turned off because of the discharge of the electric charge charged in said capacitive element, and then, when said hard circuit detects that the predetermined circuit block has not operated for a given period of time by measuring the given period of time based on an output signal of the predetermined circuit block, said hard circuit turns off said first switching element.
In one preferred embodiment of this invention, it is preferred that the hard circuit is a timer circuit. It is also preferred that the power section includes one or more battery, and that the first and second switching elements are transistors.
In this embodiment of the present invention, the power control circuit may further comprise a regulator provided between said second switching element and the predetermined circuit block for stabilizing a power-supply voltage supplied from the power section.
Further, in this embodiment of the present invention, the electronic device may be selected from a printer, a notebook type personal computer, a personal data assistant machine, a handy type game machine, and a battery-operated radio and audio equipment.
If the electronic device is a printer, the printer may be a Cycolor type printer. Also, the printer may comprise a head for exposure on which one or more light sources for emitting red light, one or more light sources for emitting green light, and one or more light sources for emitting blue light are provided. In this case, the printer is constructed to reproduce an image on a photosensitive printing paper by exposing the photosensitive printing paper by means of said head for exposure. Here, the photosensitive printing paper may contain a plurality of photosensitive microcapsules to be exposed by said head for exposure.
Moreover, the printer may further comprise: a first group of registers for setting image data corresponding to the light sources for emitting red light, image data corresponding to the light sources for emitting green light, and image data corresponding to the light sources for emitting blue light; and a second group of registers for holding the image data, which has been set in each of said first group of registers. In this case, the printer is constructed so as to set next image data in said first group of registers and to drive each of the light sources provided on the head for exposure by using the image data that is held in each of said second group of registers in parallel.
In yet another aspect of the present invention, in order to achieve the above object, the present invention is directed to a power control circuit that controls on/off of power of an electronic device including a power section, a power on/off switch and a predetermined circuit block. The power control circuit of the present invention comprises: a capacitive element connected to the power section, said capacitive element adapted to turn on a first switching element when the power on/off switch is turned on; a second switching element connected to the power section, said second switching element adapted to be turned on to supply power to the predetermined circuit block while the first switching element is turned on; and means for holding a power-on state of the first switching element when said holding means is supplied electric power from the power section via said second switching element.
In yet one more aspect of the present invention, in order to achieve the above object, the present invention is directed to a power control circuit that controls on/off of power of an electronic device including a power section and a predetermined circuit block driven by power from the power section. The power control circuit of the present invention comprises: a power on/off switch for turning on and off the power section; a capacitive element connected to said power on/off switch so that it is charged by the power section when said power on/off switch is turned off and discharged when said power on/off switch is turned on; a first switching element adapted to be turned on by an electric charge charged in said capacitive element when the power on/off switch is turned on and to be in a power-on state while the electric charge that has been charged in said capacitive element is being discharged when said power on/off switch is turned on; a second switching element provided between the power section and the predetermined circuit block for supplying electrical power from the power section to the predetermined circuit block, said second switching element adapted to be turned on and off in response to on and off of the first switching element; and means for holding the power-on state of said first switching element before said first switching element is turned off due to the discharge of the electric charge charged in the capacitive element, said holding means adapted to receive power from the power section when said second switching element is turned on by said first switching element.
In one preferred embodiment of this invention, the holding means is adapted to turn off said first switching element when it is detected that the predetermined circuit block is not being operated within a predetermined period of time.
In this embodiment of the present invention, it is preferred that the power on/off switch includes a first switch connected to the capacitive element for turning on said first switching element and a second switch provided between said first switching element and said second switching element, said first and second switches adapted to be turned on and off simultaneously.
These and other objects, structures and advantages of the present invention will be apparent from the following description of the preferred embodiment when it is considered taken in conjunction with the appended drawings.